All except Nick Xenophon (more on him later) concede that they are a citizen of a foreign county as well as being an Australian citizen. The issue that the High Court must decide is whether section 44(1) of the Australian Constitution disqualified them from being elected to Parliament because each is "a subject or a citizen ... of a foreign power".

Well, you're thinking, that's not a hard question to decide, given that they've conceded that they're dual citizens. Why, you're asking, did the Court need to hear oral arguments about this question that lasted three days?

If anything is clear, it is that Nick Xenophon will not be disqualified.

Before we talk about outcomes, here's some useful background. First, the High Court has recognised the urgency of deciding the cases quickly. Oral argument finished on 13 October, only two weeks ago. It's quite unusual for the Court to decide a case, let alone seven of them, so quickly.

Second, all seven justices of the High Court heard the seven cases. The result of each case will be determined by majority.

Third, each case is factually different from the others. So, theoretically, each justice could write a separate judgment in each case... 49 judgments! While the outcome of each case would be clear, the reasons for the outcome -- why the parliamentarian was disqualified or was not disqualified -- could be quite hard to work out.

So what are the likely results? If anything is clear, it is that Nick Xenophon will not be disqualified. That is because Andrew Tokley SC, his lead barrister, did an outstanding job of showing that the British "citizenship" that Xenophon inherited from his Cypriot father was a Claytons citizenship that gave him no real rights -- not even the right to enter the United Kingdom -- so in fact under s. 44(1) he wasn't a dual citizen.

Life is full of ironies. The irony here is that on October 6, Xenophon announced that he would resign from the Senate to run for a seat in the South Australian parliament. So the parliamentarian with the best chance of succeeding in the High Court probably cares the least about the outcome of his case.

The second thing that seems clear is that the argument originally relied on by the Government will not be upheld. The Solicitor-General (the Australian Government's barrister) started off trying to persuade the Court that the real meaning of s. 44(1) was that -- because it was designed to prevent members of Parliaments having an allegiance to a foreign country as well as to Australia -- a person who didn't even know that they were a dual citizen was not disqualified.

The rest of the pack: If a majority of the High Court uses a literal interpretation of s. 44(1), all of them will be disqualified.

This interpretation conveniently allowed Barnaby Joyce, Fiona Nash, Matt Canavan and Nick Xenophon to escape disqualification because each inherited dual citizenship through a parent and claimed not to have known about it. Also conveniently, this interpretation disqualified the two Greens senators (Waters and Ludlam) and One Nation senator Roberts because each was born overseas and therefore (according to the Government) should have known that they might be a citizen of their country of birth.

But the Government's original argument was hammered by the barrister appointed by the High Court to present opposing arguments. The law doesn't like situations where a person's rights depend on what they knew or what they believed (the law calls this situation 'subjective').

That is because there has to be a case-by-case factual inquiry about each person who might be disqualified, to determine what they actually knew/believed. Not only is this expensive and uncertain in outcome, but it would have a perverse result: It would reward careless and uninquisitive people who hadn't taken any steps to determine their citizenship (not disqualified), and penalise thoughtful and inquisitive people who had taken steps to work out whether they were dual citizens (disqualified).

Eventually, the Government's barrister retreated to a different position: That a person was disqualified by s. 44(1) only if they had done something concrete that amounted to a recognition of being a foreign citizen. This is what lawyers call an 'objective' test -- because its result depends not on what the person subjectively believed, but what they actually did. As the Government admitted to the Court, using this test would also save the Greens and the One Nation senators from disqualification.

Another route to much the same result could be based on how the High Court deals with foreign law. Traditionally, the question "Is this person/parliamentarian a citizen of Country X?" is answered by applying the law of Country X. But there are limits, as the High Court recognised in its 1992 Sykes v Cleary decision.

Say some hostile foreign power (North Korea springs to mind) decided to nobble the Australian Government by giving North Korean citizenship to all members of Parliament and thus disqualifying them all under s. 44. It's quite clear that the High Court would ignore North Korean law and would not regard the Parliament as nobbled.

You may have noticed that there's a bit of circularity involved here: What the Court in effect is saying is that it will apply foreign law to decide who is a foreign citizen, unless the result of doing this clearly would be wrong. But if you know that particular outcomes of applying foreign law are wrong, why do you need foreign law at all? You might as well just decide the question in the way that produces the right result, without consulting foreign law.

This is another way of saying that the phrase in s. 44(1) "citizen of a foreign power" doesn't involve questions of foreign law -- it's a phrase in the Australian Constitution that the High Court can give meaning to. For example, the Court could decide that a person isn't a foreign citizen unless they had taken some positive step -- like applying for a foreign passport. The Government's final position, while not suggesting that foreign law should be ignored, seems to arrive at much the same result.

So, here are the possible outcomes and their likelihood:

Nick Xenophon: Very unlikely to be disqualified.

The rest of the pack: If a majority of the High Court uses a literal interpretation of s. 44(1), all of them will be disqualified.

There is a substantial possibility that this will be the result. But it seems more likely that a majority of the Court will apply a more nuanced approach, which limits the applicability of foreign law in deciding who is a citizen of a foreign country. Under this approach, the three (Joyce, Nash and Canavan) who were born in Australia and inherited foreign citizenship) are likely not to be disqualified and the three born overseas (Ludlam, Waters and Roberts) are more at risk.